Fuel gasification system

ABSTRACT

The present invention provides a fuel gasification furnace including a gasification chamber ( 1 ) for fluidizing a high-temperature fluidizing medium therein to form a gasification chamber fluidized bed having an interface, and for gasifying a fuel in the gasification chamber fluidized bed, a char combustion chamber ( 2 ) for fluidizing a high-temperature fluidizing medium therein to form a char combustion chamber fluidized bed having an interface, and for combusting char generated by gasification in the gasification chamber ( 1 ) in the char combustion chamber fluidized bed to heat the fluidizing medium, and a first energy recovery device ( 109 ) for using gases generated by the gasification chamber ( 1 ) as a fuel. The gasification chamber ( 1 ) and the char combustion chamber ( 2 ) are integrated with each other. The gasification chamber ( 1 ) and the char combustion chamber ( 2 ) are divided from each other by a first partition wall ( 15 ) for preventing gases from flowing therebetween, and which extends vertically upward from the interfaces of the respective fluidized beds. The first partition wall ( 15 ) has a first opening ( 25 ) provided in a lower portion thereof, and the first opening ( 25 ) serves as a communication between the gasification chamber ( 1 ) and the char combustion chamber ( 2 ), for allowing the fluidizing medium heated in the char combustion chamber ( 2 ) to move from the char combustion chamber ( 2 ) via the first opening ( 25 ) into the gasification chamber ( 1 ).

This application is a divisional application of U.S. patent applicationSer. No. 09/581,593, filed Jun. 15, 2000 now allowed.

TECHNICAL FIELD

The present invention relates to a gasification furnace for gasifyingfuels including coal, municipal waste, etc., and a gasification systemwhich employs such a gasification furnace.

BACKGROUND ART

Various efforts are being made at present in various countries withrespect to highly efficient power generation systems which employ coalas fuel. For increasing power generation efficiency, it is important toconvert the chemical energy of coal into electric energy with highefficiency. However, in recent years how to develop such highlyefficient power generation systems has been looked over. The integratedgasification combined cycle (IGCC) technology converts coal into a cleanchemical energy by gasification, and then converts the chemical energydirectly into electric energy with a fuel cell or utilizes the chemicalenergy to rotate a gas turbine at a high temperature for generatingelectric energy with high efficiency. However, since the IGCC technologyis oriented toward the complete gasification of the coal, thegasification temperature needs to be increased to a temperature rangefor melting the ash, resulting in many problems related to the dischargeof the molten slag and the durability of the refractory material.Furthermore, because part of the heat energy is consumed for melting theash, although the generated gases are discharged in such a state thatthey have a high temperature, the temperature of the generated gasesmust be lowered for gas purification to a temperature of, for example,about 450° C., causing a very large sensible heat loss. Another problemis that it is necessary to supply oxygen or oxygen-enriched air in orderto achieve a high temperature stably. For these reasons, the net energyconversion efficiency is not increased, and no technology is availablefor generating electric energy with high efficiency using the generatedgases. At the present time, it has been found that the net powergeneration efficiency is not high at all.

In the integrated gasification combined cycle (IGCC), there is an upperlimit on the efficiency of the technology for finally converting thechemical energy into electric energy, resulting in a bottleneck inattempts to increase the overall efficiency. Therefore, highly efficientpower generation technology that has drawn much attention in recentyears simply generates as large an amount of gases as possible whilekeeping the temperature at the inlet of a gas turbine to an upper limitfor increasing the ratio of generated power output from the gas turbine.Typical examples of the highly efficient power generation technologyinclude a topping cycle power generation system and a power generationsystem using an improved pressurized fluidized-bed furnace.

In the power generation system using an improved pressurizedfluidized-bed furnace, coal is first gasified by a pressurizedgasification furnace, and generated unburned carbon (so-called char) iscombusted by a pressurized char combustor. After combustion gases fromthe char combustor and generated gases from the gasification furnace arecleaned, they are mixed and combusted by a topping combustor, whichproduces high-temperature gases to drive a gas turbine. It is importantin this power generation system how to increase the amount of gasesflowing into the gas turbine. The greatest one of the conditions whichimposes limitations on the increase in the flowrate of gases to the gasturbine is the cleaning of the generated gases.

For cleaning the generated gases, it is necessary to cool the generatedgases usually to about 450° C. in view of an optimum temperature for adesulfurizing reaction in a reducing atmosphere. On the other hand, thegas temperature at the inlet of the gas turbine should be as high aspossible because the efficiency of the gas turbine is enhanced as thegas temperature is higher. At present, it is an ordinal way to increasethe gas temperature at the inlet of the gas turbine to 1200° C. orslightly lower due to limitations imposed by heat resistance andcorrosion resistance of the materials for the gas turbine. Therefore,the generated gases are required to have a calorific value high enoughto increase the gas temperature from 450° C. for the gas cleaning to1200° C. at the inlet of the gas turbine.

Consequently, for the development of a power generation system using animproved pressurized fluidized-bed furnace, efforts should be made toobtain generated gases in as small an amount as possible and having ashigh a calorific value as possible. The reasons for those efforts are asfollows: If the amount of generated gases to be cleaned at 450° C. isreduced, the loss of sensible heat due to the cooling is reduced, and arequired minimum calorific value of the generated gases may be lowered.If the calorific value of the generated gases is higher than thecalorific value needed to increase the gas temperature to the requiredgas temperature at the inlet of the gas turbine, then the ratio ofcombustion air can be increased to increase the amount of gases flowinginto the gas turbine for a further increase in the efficiency of powergeneration.

In recent years, efforts to develop highly efficient waste combustionpower generation technology are being carried out in order to utilizemunicipal waste, etc. as a fuel. However, one problem of the highlyefficient waste combustion power generation technology is that since ahigh concentration of chlorine may be contained in the waste, the steamtemperature for heat recovery cannot be increased beyond 400° C. due topossible corrosion of heat transfer pipes. Therefore, there has been ademand for the development of a technology that can overcome the abovedifficulty.

One typical conventional gasification furnace which employs coal or thelike as a fuel is a twin tower circulation type gasification furnace asshown in FIG. 17 of the accompanying drawings. The two-bed pyrolysisreactor system comprises two furnaces (towers), i.e., a gasificationfurnace and a char combustion furnace. A fluidizing medium and char arecirculated between the gasification furnace and the char combustionfurnace, and a quantity of heat required for gasification is supplied tothe gasification furnace as the sensible heat of the fluidizing mediumwhich has been heated by the combustion heat of the char in the charcombustion furnace. Since gases generated in the gasification furnace donot need to be combusted, the calorific value of the generated gases canbe maintained at a high level. However, the two-bed pyrolysis reactorsystem has not actually been commercialized as a large-scale plantbecause of problems relating to the handling of high-temperatureparticles, such as obtaining a sufficient amount of particle circulationbetween the gasification furnace and the char combustion furnace,controlling of the circulating amount of particles, and stableoperation, and problems relating to operation, such as a failure intemperature control of the char combustion furnace independently ofother operations.

There has recently been proposed a system in which entire combustiongases discharged from a char combustion furnace are led to agasification furnace to make up for a shortage of heat for gasificationwhich is not fully supplied by the sensible heat of circulatingparticles, as shown in FIG. 18 of the accompanying drawings. However,inasmuch as the proposed system delivers the entire combustion gasesdischarged from the char combustion furnace to the gasification furnace,it goes against the principle of the power generation system using animproved pressurized fluidized-bed furnace that it should be obtainedgenerated gases in as small an amount as possible and having as high acalorific value as possible. That is, if the amount of char combustiongases becomes larger than an amount required for gasification orfluidization in the gasification furnace, then since the generated gasesare diluted by the excessive char combustion gases, the calorific valueis lowered, and the mixed excessive char combustion gases are alsocooled to 450° C. for gas cleaning in a reducing atmosphere, with theresult that the quantity of heat necessary to raise the gas temperatureto a proper temperature at the gas turbine inlet is increased.Conversely, if the amount of char combustion gases becomes smaller, thenthe fluidization in the gasification furnace becomes insufficient or thetemperature of the gasification furnace is lowered, resulting in a needfor supplying air to the gasification furnace. Therefore, in order forthis system to be realized, it is necessary to select coal among thelimited coal range suitable for the system. If the selected coal differseven slightly from the limited coal range, then the excessive charcombustion gases need to be cooled to 450° C., or the calorific value ofthe generated gases is lowered because of the introduction of air intothe gasification furnace, with the result that the efficiency of theoverall system will be lowered.

In this system, the temperature of the char combustion furnace iscontrolled by changing the bed height to change the heat transfer areain the bed. When the system undertakes a low load, as the combustiongases are cooled by the heat transfer pipes exposed over the bed, thetemperature of the gasification furnace and the fluidizing gas velocitychanges, affecting the gasifying reaction rate to make it difficult tooperate the system stably.

In view of the above drawbacks, the inventors of the present inventionhave devised an integrated gasification furnace comprising a singlefluidized-bed furnace which has a gasification chamber, a charcombustion chamber, and a low-temperature combustion chamber dividedthereby by partitions. The char combustion chamber, the gasificationchamber, and the low-temperature combustion chamber are disposedadjacent to each other. The inventors have invented the integratedgasification furnace in order to overcome the drawbacks of the two-bedpyrolysis reactor system described above. The integrated gasificationfurnace allows a large amount of fluidizing medium to circulate betweenthe char combustion chamber and the gasification chamber. Consequently,heat for gasification can sufficiently be supplied only by the sensibleheat of the fluidizing medium. The integrated gasification furnace ispossibly able to achieve, most easily, the principle of the powergeneration system using an improved pressurized fluidized-bed furnace sothat generated gases should be obtained in as small an amount aspossible and having as high a calorific value as possible.

Nevertheless, the integrated gasification furnace is problematic in thatsince no complete seal is provided between char combustion gases andgenerated gases, the combustion gases and the generated gases may bemixed with each other, degrading the properties of the generated gases,if the pressure balance between the gasification chamber and the charcombustion chamber is not kept well.

In the field of waste combustion power generation systems, it has beenproposed to pyrolyze the wastes and volatilize a chlorine componenttogether with volatile components, and superheat the steam with thecombustion heat of remaining char which has a greatly reduced chlorinecontent, for highly efficient power generation. However, since a smallamount of char is produced by the pyrolysis of municipal wastes, it ishighly likely not to obtain a char combustion heat required to superheatthe steam. The fluidizing medium as a heat medium and the char flow fromthe gasification furnace into the char combustion furnace, and the sameamount of fluidizing medium needs to return from the char combustionfurnace to the gasification furnace for achieving a mass balance.According to an available conventional method, the fluidizing medium hasto be mechanically delivered by a conveyor or the like, resulting inproblems such as the difficulty in handing high-temperature particlesand a large sensible heat loss.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above conventionalproblems. It is an object of the present invention to provide a fuelgasification furnace which does not need the special control of apressure balance between a gasification furnace and a char combustionfurnace, or a mechanical means for handling a fluidizing medium, whichcan stably obtain generated gases of high quality, and is capable ofhighly efficient power recovery. Another object of the present inventionis to provide an integrated gasification furnace which is capable ofreading reduced corrosion on a steam superheater (pipes), etc. and iscapable of highly efficient power generation even when a combustiblewaste material containing chlorine is used as a fuel.

To achieve the above objects, a fuel gasification system according tothe present invention comprises, as shown in FIGS. 1 and 13, agasification chamber 1 for fluidizing a high-temperature fluidizingmedium therein to form a gasification chamber fluidized bed having aninterface, and gasifying a fuel in the gasification chamber fluidizedbed. A char combustion chamber 2 is provided for fluidizing ahigh-temperature fluidizing medium therein to form a char combustionchamber fluidized bed having an interface, and combusting char generatedby gasification in the gasification chamber 1 in the char combustionchamber fluidized bed to heat the fluidizing medium. A first energyrecovery device 109 uses gases generated by the gasification chamber 1as a fuel, and the gasification chamber 1 and the char combustionchamber 2 are integrated with each other. The gasification chamber 1 andthe char combustion chamber 2 are divided from each other by a firstpartition wall 15 for preventing gases from flowing therebetweenvertically upwardly from the interfaces of the respective fluidizedbeds. The first partition wall 15 has a first opening 25 provided in alower portion thereof and serves the first opening as a communicationbetween the gasification chamber 1 and the char combustion chamber 2,for allowing the fluidizing medium heated in the char combustion chamber2 to move from the char combustion chamber 2 via the first opening intothe gasification chamber.

With the above arrangement, since the gasification chamber and the charcombustion chamber are integrated with each other, the fluidizing mediumcan be handled with ease between the gasification chamber and the charcombustion chamber. Since the gasification chamber and the charcombustion chamber are divided from each other by the first partitionwall for preventing gases from flowing therebetween upwardly of theinterfaces of the respective fluidized beds, the gases generated in thegasification chamber and the combustion gases in the char combustionchamber are not almost mixed with each other. Since the energy recoverydevice, which is a power recovery device such as a gas turbine, isprovided, the power or energy can be recovered in such a way as to drivea fluid machine such as an air compressor or a generator.

The fluidized bed in the fuel gasification system according to theinvention comprises a dense bed, positioned in a vertically lowerregion, which contains a high concentration of fluidizing medium, and asplash zone, positioned vertically above the dense bed, which containsboth the fluidizing medium and a large amount of gases. Above thefluidized bed (i.e., above the splash zone) there is positioned afreeboard which contains almost no fluidizing medium, but is primarilymade up of gases. The interface according to the present inventionrefers to a splash zone having a certain thickness. However, theinterface may be understood as a hypothetical plane positionedintermediate between an upper surface of the splash zone and a lowersurface of the splash zone (upper surface of the dense bed). Preferably,the chambers are divided from each other by the partition wall such thatno gases flow therebetween upwardly of the dense bed.

In the fuel gasification system of the present invention, thegasification chamber 1 and the char combustion chamber 2 are divided(separated) from each other by a second partition wall 11 for preventinggases from flowing therebetween vertically upward from the interfaces ofthe respective fluidized beds. The second partition wall 11 has a secondopening 21 provided in a lower portion thereof and serves the secondopening as a communication between the gasification chamber 1 and thechar combustion chamber 2, for allowing the fluidizing medium heated tomove from the gasification chamber 1 via the second opening 21 into thechar combustion chamber 2.

With the above arrangement, since the fluidizing medium moves from thegasification chamber 1 via the second opening 21 into the charcombustion chamber 2, when char is generated in the gasification chamber1, the char moves, together with the fluidizing medium, into the charcombustion chamber 2, and a mass balance of the fluidizing mediumbetween the gasification chamber 1 and the char combustion chamber 2 ismaintained.

The above fuel gasification system further comprises a heat recoverychamber 3 integrated with the gasification chamber 1 and the charcombustion chamber 2. The gasification chamber 1 and the heat recoverychamber 2 are divided from each other or are not in contact with eachother so that gases will not flow directly therebetween. With thisarrangement, heat can be recovered without causing the gases generatedin the gasification chamber and the combustion gases in the heatrecovery chamber to be mixed with each other. The heat recovery chamberis provided, and even when the amount of char generated in thegasification chamber and the amount of char required to heat thefluidizing medium in the char combustion chamber is out of balance, thedifference between the amounts can be adjusted by increasing or reducingthe amount of heat recovered in the heat recovery chamber.

The fuel combustion chamber described above may comprise a boiler 111for being supplied with the gases used as the fuel in the first energyrecovery device 109 and combustion gases from the char combustionchamber 2. Typically, the first energy recovery device is a gas turbineunit 109 or its gas turbine 106, and the gases used as the fuel arewaste gases combusted in a combustor 105 of the gas turbine unit andfrom which energy is recovered by the gas turbine 106. Since the wastegases contain a considerable amount of heat energy, the heat energy isrecovered by the boiler 111.

In the above system, an oxygen-free gas should preferably be used as thefluidizing gas in the gasification chamber 1. The oxygen-free gas refersto a gas which contains a small amount of oxygen, and whose oxygenconcentration is not large enough to substantially combust the gasesgenerated in the gasification furnace. Because the oxygen-free gas isused, the generated gases are not substantially combusted, and have ahigh calorific value.

As shown in FIG. 14, the gasification chamber and the char combustionchamber are pressurized to a pressure higher than an atmosphericpressure. The fuel gasification system further comprises a second energyrecovery device 141 driven by combustion gases from the char combustionchamber 2, and a boiler 111 for being supplied with the waste gases usedas the fuel in the first energy recovery device 109 and combustion gasesfrom the second energy recovery device 141.

With the above arrangement, since the combustion gases from the charcombustion chamber have a pressure energy in addition to a temperatureenergy, the second energy recovery device, typically a power recoveryturbine having the same structure as the gas turbine in the gas turbineunit, can recover power from the combustion gases. The gases generatedin the gasification chamber can be led directly to the combustor 105 ofthe gas turbine unit, without passing through a gas compressor, and thecombustion gases from the combustor 105 are introduced into the gasturbine 106 of the gas turbine unit for generating power. Therefore, thegas compressor combined with the gas turbine may be dispensed with.However, if there is a difference between the pressure required for thegas turbine and the pressure of the generated gases, then a gascompressor may be provided for generating a pressure to compensate forthe pressure difference.

To achieve the above object, a fuel gasification system according to thepresent invention comprises, as shown in FIGS. 1 and 11, a gasificationchamber 1 for fluidizing a high-temperature fluidizing medium therein toform a gasification chamber fluidized bed having an interface, andgasifying a fuel in the gasification chamber fluidized bed. A charcombustion chamber 2 is provided for fluidizing a high-temperaturefluidizing medium therein to form a char combustion chamber fluidizedbed having an interface, and combusting char generated by gasificationin the gasification chamber 1 in the char combustion chamber fluidizedbed to heat the fluidizing medium and generate combustion gases. Astabilizing combustion chamber 53 is provided for combusting gasesgenerated in the gasification chamber 1 to heat the combustion gasesgenerated in the char combustion chamber 2, and an energy recoverydevice 55 recovers energy from the combustion gases heated in thestabilizing combustion chamber 53. The gasification chamber 1 and thechar combustion chamber 2 are integrated with each other and pressurizedto a pressure higher than an atmospheric pressure. The gasificationchamber 1 and the char combustion chamber 2 are divided from each otherby a first partition wall 15 for preventing gases from flowingtherebetween vertically upward of the interfaces of the respectivefluidized beds. The first partition wall 15 has a first opening 25provided in a lower portion thereof, and the first opening 25 serves asa communication between the gasification chamber 1 and the charcombustion chamber 2, for allowing the fluidizing medium heated in thechar combustion chamber 2 to move from the char combustion chamber 2 viathe first opening 25 into the gasification chamber 1.

With the above arrangement, since the gasification chamber 1 and thechar combustion chamber 2 are integrated with each other and pressurizedto a pressure higher than an atmospheric pressure, the partial pressureof oxygen in the char combustion chamber can be increased to maintain agood combustion state, and energy can be recovered from the combustiongases from the char combustion chamber by the energy recovery device,which comprises a power recovery turbine, for example. When thegenerated gases from the gasification chamber are combusted in thestabilizing combustion chamber, the combustion gases from the charcombustion chamber can be heated to a high temperature of 1200° C., forexample. Therefore, power can be recovered highly efficiently by thepower recovery turbine.

In the fuel gasification system described above, the gasificationchamber 1 and the char combustion chamber 2 are divided from each otherby a second partition wall 11 for preventing gases from flowingtherebetween vertically upwardly from the interfaces of the respectivefluidized beds. The second partition wall 11 has a second opening 21provided in a lower portion thereof and the second opening serves as acommunication between the gasification chamber 1 and the char combustionchamber 2, for allowing the fluidizing medium heated to move from thegasification chamber 1 via the second opening 21 into the charcombustion chamber 2.

The fuel gasification system described above further comprises a heatrecovery chamber 3 integrated with the gasification chamber 1 and thechar combustion chamber 2, and the gasification chamber 1 and the heatrecovery chamber 3 are divided from each other or are not in contactwith each other so that gases will not flow directly therebetween.

The fuel gasification system described above further comprises a boiler58 for being supplied with the gases from which the energy is recoveredby the energy recovery device 58. Even after the energy is recovered bythe energy recovery device 58, heat can be recovered from waste gaseswhich contain heat energy by the boiler.

As shown in FIGS. 15 and 16, in the fuel gasification system describedabove, the boiler 58 may combust a fuel other than the gases suppliedthereto. Even when the amount of heat required for the boiler and theamount of heat supplied from the char combustion chamber are brought outof balance, the difference can be compensated for by the other fuel.Therefore, an existing boiler 131 may be used as the boiler.

To achieve the above object, a method of repowering an existing boileraccording to the present invention comprises, as shown in FIG. 15 or 16,the steps of providing an existing boiler 131; and providing a fuelgasification system as described above for supplying combustion gases tothe existing boiler 131.

According to the above method, the fuel gasification system is connectedto the existing boiler for supplying combustion gases to the existingboiler. Consequently, a boiler which has low efficiency and discharges alarge amount of carbon dioxide gas, such as an existing boiler whichuses pulverized coal as a fuel, can be modified, i.e., repowered, into ahighly efficient energy generating system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the basic concept of an integratedgasification furnace according to the present invention;

FIG. 2 is a schematic diagram showing a modification of the integratedgasification furnace shown in FIG. 1, with a slanted furnace bottom anda partition wall having a bulge;

FIGS. 3A and 3B are schematic diagrams showing a pressure controlfunction of the integrated gasification furnace according to the presentinvention;

FIG. 4 is a view showing a cylindrical furnace which embodies theintegrated gasification furnace according to the present invention;

FIG. 5 is a horizontal cross-sectional view of a fluidized bed of thecylindrical furnace shown in FIG. 4;

FIG. 6 is a horizontal cross-sectional view showing a modification ofthe fluidized bed shown in FIG. 5;

FIG. 7 is a horizontal cross-sectional view of a rectangular furnacewhich embodies the integrated gasification furnace according to thepresent invention;

FIG. 8 is a horizontal cross-sectional view showing a modification ofthe rectangular furnace shown in FIG. 7;

FIG. 9 is a schematic diagram of a normal-pressure-type integratedgasification furnace according to the present invention;

FIG. 10 is a schematic diagram of a combined cycle power generationsystem which employs the integrated gasification furnace shown in FIG.9;

FIG. 11 is a schematic diagram of a combined cycle power generationsystem which employs the integrated gasification furnace according tothe present invention;

FIG. 12 is a schematic diagram showing a modification of the combinedcycle power generation system shown in FIG. 11;

FIG. 13 is a schematic diagram showing a system for recovering powerfrom generated gases from a normal-pressure-type integrated gasificationfurnace;

FIG. 14 is a schematic diagram showing a system for recovering powerfrom generated gases from a pressurized-type integrated gasificationfurnace;

FIG. 15 is a schematic diagram showing a system which is a combinationof the system for recovering power from generated gases from thenormal-pressure-type integrated gasification furnace and an existingboiler;

FIG. 16 is a schematic diagram showing a system which is a combinationof the system for recovering power from generated gases from thepressurized-type integrated gasification furnace and an existing boiler;

FIG. 17 is a schematic diagram of a conventional two-bed pyrolysisreactor system; and

FIG. 18 is a schematic diagram of a combined cycle power generationsystem which employs a conventional fluidized-bed furnace.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below withreference to FIGS. 1 through 16.

FIG. 1 schematically shows the basic structure of a gasification furnaceaccording to the present invention. An integrated gasification furnace101 according to the embodiment shown in FIG. 1 has a gasificationchamber 1, a char combustion chamber 2, and a heat recovery chamber 3for performing three respective functions of pyrolysis (i.e.,gasification), char combustion, and heat recovery, the chambers beinghoused in a furnace which is cylindrical or rectangular, for example, inshape. The gasification chamber 1, the char combustion chamber 2, andthe heat recovery chamber 3 are divided by partition walls 11, 12, 13,14, 15 to form fluidized beds, each comprising a dense bed containing afluidizing medium, in respective bottoms. Gas diffusers for blowingfluidizing gases into the fluidizing medium are disposed on the furnacebottom of the chambers 1, 2, 3 for causing the fluidizing medium to befluidized in the fluidized beds in the chambers 1, 2, 3 (i.e., thegasification chamber fluidized bed, the char combustion chamberfluidized bed, and the heat recovery chamber fluidized bed). Each of thegas diffusers comprises a porous plate, for example, placed on thefurnace bottom. The gas diffuser is divided into a plurality ofcompartments. In order to change the space velocity at various parts ineach of the chambers, the speed of the fluidizing gases discharged fromthe compartments of the gas diffusers through the porous plates ischanged. Since the gas velocity differs relatively from part to part inthe chambers, the fluidizing medium in the chambers flows in differentconditions in the parts of the chambers, thus developing internalrevolving flow patterns. In FIG. 1, the sizes of blank arrows in the gasdiffusers represent the velocity of the discharged fluidizing gases. Forexample, thick arrows in areas indicated by 2 b represent a highervelocity of the discharged fluidizing gases than a thin arrow in thearea indicated by 2 a.

The gasification chamber 1 and the char combustion chamber 2 are dividedfrom each other by the partition wall 11, the char combustion chamber 2and the heat recovery chamber 3 are divided from each other by thepartition wall 12, and the gasification chamber 1 and the heat recoverychamber 3 are divided from each other by the partition wall 13. Thesechambers are not installed as separate furnaces, but installed as asingle furnace. In the gasification furnace 101, the partition wall 11serves as a second partition wall according to the present invention. Asettling char combustion chamber 4 for settling the fluidizing mediumtherein is disposed near a portion of the char combustion chamber 2which is in contact with the gasification chamber 1. Thus, the charcombustion chamber 2 is separated into the settling char combustionchamber 4 and another portion of the char combustion chamber 2 (mainchar combustion chamber). The settling char combustion chamber 4 isdivided from the char combustion chamber 2 (main char combustionchamber) by the partition wall 14. The settling char combustion chamber4 and the gasification chamber 1 are divided from each other by thepartition wall 15 which serves as a first partition wall according tothe present invention.

A fluidized bed and an interface will be described below. The fluidizedbed comprises a dense bed, positioned in a vertically lower region,which contains a high concentration of fluidizing medium (e.g., silicasand) that is held in a fluidizing state by the fluidizing gas, and asplash zone, positioned vertically above the dense bed, which containsboth the fluidizing medium and a large amount of gases, with thefluidizing medium splashing violently. Above the fluidized bed (i.e.,above the splash zone), there is positioned a freeboard which containsalmost no fluidizing medium, but is primarily made up of gases. Theinterface according to the present invention refers to a splash zonehaving a certain thickness. Otherwise, the interface may be understoodas a hypothetical plane positioned intermediate between an upper surfaceof the splash zone and a lower surface of the splash zone (upper surfaceof the dense bed).

Furthermore, with respect to a statement “chambers are divided from eachother by a partition wall so as not to allow gases to flow verticallyupward from an interface of a fluidized bed”, it is preferable that nogases flow above the upper surface of the dense bed below the interface.

The partition wall 11 between the gasification chamber 1 and the charcombustion chamber 2 extends substantially fully from a ceiling 19 ofthe furnace to the furnace bottom (the porous plates of the gasdiffusers). However, the partition wall 11 has a lower end that is notin contact with the furnace bottom, and has a second opening 21 near thefurnace bottom. However, the opening 21 has an upper end which does notextend upwardly from either one of the gasification chamber fluidizedbed interface and the char combustion chamber fluidized bed interface.Preferably, the upper end of the opening 21 does not extend upwardlyfrom either one of the upper surface of the dense bed of thegasification chamber fluidized bed and the upper surface of the densebed of the char combustion chamber fluidized bed. That is to say, theopening 21 should preferably be arranged so as to be submerged in thedense bed at all times. Thus, the gasification chamber 1 and the charcombustion chamber 2 are divided from each other by the partition wallsuch that no gases flow therebetween at least in the freeboard, orupwardly from the interface, or more preferably upwardly from the uppersurface of the dense bed.

The partition wall 12 between the char combustion chamber 2 and the heatrecovery chamber 3 has an upper end located near the interface (i.e.,above the upper surface of the dense bed), but positioned downwardlyfrom the upper surface of the splash zone. The partition wall 12 has alower end extending toward the vicinity of the furnace bottom, but notbeing in contact with the furnace bottom as is the case with thepartition wall 11. The partition wall 12 has an opening 22 near thefurnace bottom, which does not extend above the upper surface of thedense bed.

The partition wall 13 between the gasification chamber 1 and the heatrecovery chamber 3 extends fully from the furnace bottom to the furnaceceiling. The partition wall 14 which divides the char combustion chamber2 to provide the settling char combustion chamber 4 has an upper endlocated near the interface of the fluidized bed and a lower end incontact with the furnace bottom. The relationship between the upper endof the partition wall 14 and the fluidized bed is the same as therelationship between the partition wall 12 and the fluidized bed. Thepartition wall 15 which divides the settling char combustion chamber 4and the gasification chamber 1 from each other is the same as thepartition wall 11. The partition wall 15 extends fully from the furnaceceiling to the furnace bottom. However, the partition wall 15 has alower end that is not in contact with the furnace bottom, and has afirst opening 25 near the furnace bottom. The opening 25 has an upperend which is positioned below the upper surface of the dense bed.Therefore, the relationship between the first opening 25 and thefluidized bed is the same as the relationship between the second opening21 and the fluidized bed.

A fuel including coal, waste, etc. charged into the gasification chamberis heated by the fluidizing medium, and pyrolyzed and gasified.Typically, the fuel is not combusted, but carbonized, in thegasification chamber 1. Remaining carbonized char and the fluidizingmedium flow into the char combustion chamber 2 through the opening 21 inthe lower portion of the partition wall 11. The char thus introducedfrom the gasification furnace 1 is combusted in the char combustionchamber 2 to heat the fluidizing medium. The fluidizing medium heated bythe combustion heat of the char in the char combustion chamber 2 flowsbeyond the upper end of the partition wall 12 into the heat recoverychamber 3. In the heat recovery chamber 3, the heat of the fluidizingmedium is removed by a submerged heat transfer pipe 41 disposed belowthe interface in the heat recovery chamber 3, so that the fluidizingmedium is then cooled. The fluidizing medium then flows through thelower opening 22 in the partition wall 12 into the char combustionchamber 2.

Volatile components of the combustibles charged into the gasificationchamber 1 are instantaneously gasified, and then solid carbon (char) isgasified relatively slowly. Therefore, the retention time of the char inthe gasification chamber 1, i.e., from the time when the char is chargedinto the gasification chamber to the time when the char flows into thecombustion chamber 2, can be an important factor for determining thegasification rate of the fuel (carbon conversion efficiency).

When silica sand is used as the fluidizing medium, since the specificgravity of char is smaller than the specific gravity of the fluidizingmedium, the char is accumulated mainly in an upper portion of the bed.If the furnace is of such a structure that the fluidizing medium flowsinto the gasification chamber and flows from the gasification chamberinto the char combustion chamber through the lower opening in thepartition wall, then the fluidizing medium that is present mainly in alower portion of the bed can flow more easily from the gasificationchamber into the char combustion chamber than the char present mainly inthe upper portion of the bed. Conversely, the char can flow less easilyfrom the gasification chamber into the char combustion chamber.Therefore, it is possible to keep the average retention time of the charin the gasification chamber longer than if a completely mixed bed weredeveloped in the gasification chamber.

The fluidizing medium flowing from the settling char combustion chamber4 into the gasification chamber 1 is not mixed well with the bed in thegasification chamber 1, but flows mainly through a lower portion of thegasification chamber 1 into the char combustion chamber 2. Even in thiscase, the fluidizing gas supplied from the gasification chamber bottomand the fluidizing medium perform a heat exchange to transfer heat fromthe fluidizing gas to the char, so that the heat for gasifying the charcan be supplied indirectly from the sensible heat of the fluidizingmedium.

Furthermore, it is possible to change the mixed condition of thefluidizing medium and the char in the gasification chamber by adjustingthe flowrate of the fluidizing gas in the gasification chamber tocontrol the state of the revolving flows in the gasification chamber,for thereby controlling the average retention time of the char in thegasification chamber.

With the furnace structure according to the present invention, theheight of the fluidized bed in the gasification chamber can freely bechanged by controlling the pressure difference between the gasificationchamber and the char combustion chamber. It is possible to control theaverage holding time of the char in the gasification chamber accordingto this method.

The heat recovery chamber 3 is not indispensable for the fuelgasification system according to the present invention. Specifically, ifthe amount of char, composed mainly of carbon, remaining after thevolatile components are gasified in the gasification chamber 1 and theamount of char required to heat the fluidizing medium in the charcombustion chamber 2 are nearly equal to each other, then the heatrecovery chamber 3 which deprives the fluidizing medium of heat is notnecessary. If the difference between the above amounts of char is small,then the gasifying temperature in the gasification chamber 1 becomeshigher, resulting in an increase in the amount of a, CO gas generated inthe gasification chamber 1, so that a carbon balance will be kept in thegasification chamber 1.

In the case that the heat recovery chamber 3 shown in FIG. 1 isemployed, the integrated gasification furnace is capable of handling awide variety of fuels ranging from coal which produces a large amount ofchar to municipal waste which produces a little amount of char.Therefore, irrespective of whatever fuel may be used, the combustiontemperature in the char combustion chamber 2 can appropriately beadjusted to keep the temperature of the fluidizing medium adequate bycontrolling the amount of heat recovered in the heat recovery chamber 3.

The fluidizing medium which has been heated in the char combustionchamber 2 flows beyond the upper end of the fourth partition wall 14into the settling char combustion chamber 4, and then flows through theopening 25 in the lower portion of the partition wall 15 into thegasification chamber 1.

The flowing state and movement of the fluidizing medium between thechambers will be described below.

A region in the gasification chamber 1 which is near and in contact withthe partition wall 15 between the gasification chamber 1 and thesettling char combustion chamber 4 serves as a strongly fluidized region1 b where a fluidized state is maintained more vigorously than thefluidized state in the settling char combustion chamber 4. The velocityof the fluidizing gases may be varied from place to place in order topromote the mixing and diffusion of the charged fuel and the fluidizingmedium. For example, as shown in FIG. 1, a weakly fluidized region 1 amay be produced in addition to the strongly fluidized region 1 b forforming revolving flows.

The char combustion chamber 2 has a central weakly fluidized region 2 aand a peripheral strongly fluidized region 2 b therein, causing thefluidizing medium and the char to form internal revolving flows. It ispreferable that the fluidizing velocity of the gas in the stronglyfluidized regions in the gasification chamber 1 and the char combustionchamber 2 be 5 Umf or higher, and the fluidizing velocity of the gas inthe weakly fluidized regions therein be 5 Umf or lower. However, thefluidizing velocities of the gas may exceed these ranges if a relativeclear difference is provided between the fluidizing velocity in theweakly fluidized region and the fluidizing velocity in the stronglyfluidized region. The strongly fluidized region 2 b may be arranged inregions in the char combustion chamber 2 which contact the heat recoverychamber 3 and the settling char combustion chamber 4. If necessary, thefurnace bottom may have such a slope that the furnace bottom goes downfrom the weakly fluidized region toward the strongly fluidized region(FIG. 2). Here, “Umf” represents the minimum fluidizing velocity (thegas velocity at which fluidization begins) of the fluidized medium.Therefore, 5 Umf represents a velocity which is five times the minimumfluidizing velocity of the fluidized medium.

As described above, the fluidized state in the char combustion chamber 2near the partition wall 12 between the char combustion chamber 2 and theheat recovery chamber 3 is relatively stronger than the fluidized statein the heat recovery chamber 3. Therefore, the fluidizing medium flowsfrom the char combustion chamber 2 into the heat recovery chamber 3beyond the upper end of the partition wall 12 which is positioned nearthe interface of the fluidized bed. The fluidizing medium that hasflowed into the heat recovery chamber 3 moves downwardly (toward thefurnace bottom) because of the relatively weakly fluidized state, i.e.,the highly dense state, in the heat recovery chamber 3, and then movesfrom the heat recovery chamber 3 through the opening 22 in the lower endof the partition wall 12 near the furnace bottom and into the charcombustion chamber 2.

Similarly, the fluidized state in the major part of the char combustionchamber 2 near the partition wall 14 between the major part of the charcombustion chamber 2 and the settling char combustion chamber 4 isrelatively stronger than the fluidized state in the settling charcombustion chamber 4. Therefore, the fluidizing medium flows from themajor part of the char combustion chamber 2 into the settling charcombustion chamber 4 beyond the upper end of the partition wall 14 whichis positioned near the interface of the fluidized bed. The fluidizingmedium that has flowed into the settling char combustion chamber 4 movesdownwardly (toward the furnace bottom) because of the relatively weaklyfluidized state, i.e., the highly dense state, in the settling charcombustion chamber 4, and then moves from the settling char combustionchamber 4 through the opening 25 in the lower end of the partition wall15 near the furnace bottom into the gasification chamber 1. Thefluidized state in the gasification chamber 1 near the partition wall 15between the gasification chamber 1 and the settling char combustionchamber 4 is relatively stronger than the fluidized state in thesettling char combustion chamber 4. This relatively strong fluidizedstate induces the fluidizing medium to move from the settling charcombustion chamber 4 into the gasification chamber 1.

Similarly, the fluidized state in the char combustion chamber 2 near thepartition wall 11 between the gasification chamber 1 and the charcombustion chamber 2 is relatively stronger than the fluidized state inthe gasification chamber 1. Therefore, the fluidizing medium flowsthrough the opening 21 (submerged in the dense bed) in the partitionwall 11 below the interface of the fluidized bed, preferably below theupper surface of the dense bed, into the char combustion chamber 2.

Generally, if two chambers A, B are divided from each other by apartition wall X whose upper end is positioned near the interface, afluidizing medium moves between the two chambers A, B depending on thefluidized states in the chambers A, B near the partition wall X. Forexample, when the fluidized state in the chamber A is stronger than thefluidized state in the chamber B, the fluidizing medium flows from thechamber A into the chamber B beyond the upper end of the partition wallX. If chambers A, B are divided from each other by a partition wall Ywhose lower end (submerged in the dense bed) is positioned below theinterface, preferably below the upper surface of the dense bed, that is,by a partition wall Y which has an opening positioned below theinterface or submerged in the dense bed, a fluidizing medium movesbetween the two chambers A, B depending on the fluidizing intensity inthe chambers A, B near the partition wall Y. For example, when thefluidized state in the chamber A is stronger than the fluidized state inthe chamber B, the fluidizing medium flows from the chamber B into thechamber A through the opening in the lower end of the partition wall Y.The movement of the fluidizing medium may be induced by the relativelystrongly fluidized state of the fluidizing medium in the chamber A, orby the higher density of the fluidizing medium in the relatively weaklyfluidized state in the chamber B than the density of the fluidizingmedium in the chamber A. When the above movement of the fluidizingmedium between the chambers occurs in one place, the mass balancebetween the chambers tend to be lost, but the fluidizing medium iscaused to move between the chambers in another place in order to keepthe mass balance.

With respect to a partition which defines one chamber and the relativerelationship between the upper end of the partition wall X and the lowerend of the partition wall Y, the upper end of the partition wall Xbeyond which the fluidizing medium moves is positioned vertically abovethe lower end of partition wall Y below which the fluidizing mediummoves. By arranging the above structure, when the fluidizing mediumfills the chamber and is fluidized, and the amount of fluidizing mediumfilling the chamber is appropriately determined, the upper end can bepositioned near the interface of the fluidized bed and the lower end canbe positioned so as to be submerged in the dense bed. By appropriatelysetting up the intensity of the fluidization near the partition wall asdescribed above, the fluidizing medium can be moved in a desireddirection with respect to the partition wall X or the partition wall Y,and the flow of gases between the two chambers divided from each otherby the partition wall Y can be eliminated.

The above method is applied to the gasification furnace shown in FIG. 1as follows: The char combustion chamber 2 and the heat recovery chamber3 are divided from each other by the partition wall 12 whose upper endis positioned near the height of the interface and lower end submergedin the dense bed, and the fluidized state in the char combustion chamber2 near the partition wall 12 is stronger than the fluidized state in theheat recovery chamber 3 near the partition wall 12. Therefore, thefluidizing medium flows from the char combustion chamber 2 into the heatrecovery chamber 3 beyond the upper end of the partition wall 12, andthen moves from the heat recovery chamber 3 under the lower end of thepartition wall 12 into the char combustion chamber 2.

The char combustion chamber 2 and the gasification chamber 1 are dividedfrom each other by the partition wall 15 whose lower end is submerged inthe dense bed. The settling char combustion chamber 4 is disposed in thechar combustion chamber 2 near the partition wall 15, and the settlingchar combustion chamber 4 is surrounded by the partition wall 14 whoseupper end is positioned near the height of the interface and thepartition wall 15. The fluidized state in the major part of the charcombustion chamber 2 near the partition wall 14 is stronger than thefluidized state in the settling char combustion chamber 4 near thepartition wall 14. Therefore, the fluidizing medium flows from the majorpart of the char combustion chamber 2 into the settling char combustionchamber 4 beyond the upper end of the partition wall 14. With thisarrangement, the fluidizing medium which has flowed into the settlingchar combustion chamber 4 moves from the settling char combustionchamber 4 under the lower end of the partition wall 15 into thegasification chamber 1 in order to maintain a mass balance at least. Atthis time, if the fluidized state in the gasification chamber 1 near thepartition wall 15 is stronger than the fluidized state in the settlingchar combustion chamber 4 near the partition wall 15, then the movementof the fluidizing medium is promoted by an inducing function.

The gasification furnace 1 and the major part of the char combustionchamber 2 are divided from each other by the second partition wall 11whose lower end is submerged in the dense bed. The fluidizing mediumwhich has moved from the settling char combustion chamber 4 into thegasification furnace 1 moves under the lower end of the partition wall11 into the char combustion chamber 2 in order to maintain theaforementioned mass balance. At this time, if the fluidized state in thechar combustion chamber 2 near the partition wall 11 is stronger thanthe fluidized state in the gasification furnace 1 near the partitionwall 11, then the fluidizing medium moves not only to maintain theaforementioned mass balance, but also is induced to move into the charcombustion chamber 2 due to the strongly fluidized state.

In the embodiment shown in FIG. 1, the fluidizing medium descends in thesettling char combustion chamber 4 which is part of the char combustionchamber 2. A similar structure may be provided as a settlinggasification chamber (not shown) in part of the gasification chamber 1,specifically, at the opening 21. That is, the fluidized state in thesettling gasification chamber is made relatively weaker than thefluidized state in the major part of the gasification chamber to causethe fluidizing medium in the major part of the gasification chamber toflow beyond the upper end of the partition wall into the settlinggasification chamber, and the settled fluidizing medium moves throughthe opening 21 into the char combustion chamber. At this time, thesettling char combustion chamber 4 may be, or may not be, providedtogether with the settling gasification chamber. By employing thesettling gasification chamber, as is the case of the gasificationfurnace shown in FIG. 1, the fluidizing medium moves from the charcombustion chamber 2 through the opening 25 into the gasificationchamber 1, and then moves from the gasification chamber 1 through theopening 21 into the char combustion chamber 2.

The heat recovery chamber 3 is uniformly fluidized, and usuallymaintained in a fluidized state which is, at maximum, weaker than thefluidized state in the char combustion chamber 2 in contact with theheat recovery chamber. The velocity of the fluidizing gases in the heatrecovery chamber 3 is controlled to be in a range from 0 to 3 Umf, andthe fluidizing medium is fluidized weakly, forming a settled fluidizedlayer. The space velocity 0 Umf represents that the fluidizing gases isstopped. In this manner, the heat recovery in the heat recovery chamber3 can be minimized. That is, the heat recovery chamber 3 is capable ofadjusting the amount of recovered heat in a range from maximum tominimum levels by changing the fluidized state of the fluidizing medium.In the heat recovery chamber 3, the fluidization can be initiated andstopped, or adjusted in its intensity uniformly throughout the wholechamber, the fluidization can be stopped in a certain area of thechamber and performed in the other area, or the fluidization in thecertain area of the chamber can be adjusted in its intensity.

All the partition walls between the chambers are ordinarily verticalwalls. If necessary, a partition wall may have a bulge. For example, asshown in FIG. 2, the partition walls 12, 14 may have bulges 32 near theinterface of the fluidized bed in the char combustion chamber 2 forchanging the direction of flow of the fluidizing medium near thepartition walls to promote the internal revolving flows. Relativelylarge incombustibles contained in the fuel are discharged from anincombustible discharge port 33 provided in the furnace bottom of thegasification chamber 1. The furnace bottom in each of the chambers maybe horizontal, but the furnace bottom may be slanted along the flowpatterns of the fluidizing medium in the vicinity of the furnace bottomso that the flow of the fluidizing medium will not be kept stagnant, asshown in FIG. 2. An incombustible discharge port may be provided in notonly the furnace bottom of the gasification chamber 1, but also thefurnace bottom of the char combustion chamber 2 or the heat recoverychamber 3.

Most preferably, the fluidizing gas in the gasification chamber 1comprises a compressed generated gas in recycled use. In the case thatthe fluidizing gas comprises a generated gas, the gas discharged fromthe gasification chamber is the gas generated only from the fuel, andhence a gas of very high quality can be obtained. In the case that thefluidizing gas cannot be a generated gas, it may comprise a gascontaining as little oxygen as possible (oxygen-free gas), such as watersteam or the like. If the bed temperature of the fluidizing medium islowered due to the endothermic reaction upon gasification, then oxygenor an oxygen containing gas, e.g., air, may be supplied, in addition tothe oxygen-free gas, to combust part of the generated gas. Thefluidizing gas supplied to the char combustion chamber 2 comprises anoxygen containing gas, e.g., air or a mixed gas of oxygen and steam,required to combust the char. The fluidizing gas supplied to the heatrecovery chamber 3 comprises air, water steam, a combustion exhaust gas,or the like.

Areas above the surfaces of the fluidized beds (the upper surfaces ofthe splash zones) in the gasification furnace 1 and the char combustionchamber 2, i.e., the freeboards, are completely divided by the partitionwalls. More specifically, areas above the surfaces of the dense beds ofthe fluidized beds, i.e., the splash zones and the freeboards, arecompletely divided by the partition walls. Therefore, as shown in FIGS.3A and 3B, even when the pressures P1, P2 in the char combustion chamber2 and the gasification furnace 1 are brought out of balance, thepressure difference can be absorbed by a slight change in the differencebetween the positions of the interfaces of the fluidized beds in thechambers, or the difference between the positions of the surfaces of thedense beds (i.e., the bed height difference. Specifically, since thegasification furnace 1 and the char combustion chamber 2 are dividedfrom each other by the partition wall 15, even when the pressures P1, P2in these chambers are varied, the pressure difference can be absorbed bythe bed height difference until either one of the beds is lowered to theupper end of the opening 25. Therefore, an upper limit for the pressuredifference (P1−P2 or P2−P1) between the freeboards in the charcombustion chamber 2 and the gasification furnace 1 which can beabsorbed by the bed height difference is substantially equal to thedifference between the head of the gasification chamber fluidized bedfrom the upper end of the opening 25 and the head of the char combustionchamber fluidized bed from the upper end of the opening 25.

In the integrated gasification furnace 101 according to the embodimentdescribed above, the three chambers, i.e., the gasification chamber, thechar combustion chamber, and the heat recovery chamber, which aredivided from each other by the partition walls, are disposed in onefluidized-bed furnace, with the char combustion chamber and thegasification chamber being positioned adjacent to each other, and thechar combustion chamber and the heat recovery chamber being positionedadjacent to each other. Inasmuch as the integrated gasification furnace101 differs from the two-bed pyrolysis reactor system in that a largeamount of fluidizing medium can be circulated between the charcombustion chamber and the gasification chamber, the quantity of heatfor gasification can sufficiently be supplied only by the sensible heatof the fluidizing medium. It is, therefore, possible to realize, withutmost ease, the principle of the power generation system using animproved pressurized fluidized-bed furnace so that it is possible toobtain generated gases in as small an amount as possible and having ashigh a calorific value as possible.

In this embodiment, since a complete seal is provided between charcombustion gases and generated gases, the pressure balance between thegasification chamber and the char combustion chamber is controlled wellwithout causing the combustion gases and the generated gases to be mixedwith each other and degrading the properties of the generated gases.

The fluidizing medium as the heat medium and the char flow from thegasification chamber 1 into the char combustion chamber 2, and the sameamount of fluidizing medium returns from the char combustion chamber 2to the gasification chamber 1. Therefore, input and output of thefluidizing medium is naturally balanced. It is not necessary tomechanically deliver, with a conveyor or the like, the fluidizing mediumfrom the char combustion chamber 2 back into the gasification chamber 1.Therefore, the present embodiment is free of the difficulty in handlinghigh-temperature particles and a large sensible heat loss.

As described above, according to the present embodiment as shown in FIG.1, in the integrated gasification furnace having three functions ofpyrolysis and gasification of the fuel, char combustion, and submergedheat recovery coexistent in one fluidized-bed furnace, for supplying ahigh-temperature fluidizing medium in the char combustion chamber as theheat medium to supply a heat source for pyrolysis and gasification tothe gasification chamber, the gasification chamber and the heat recoverychamber are fully divided from each other by the partition wallextending from the furnace bottom to the ceiling or provided so as notto be in contact with each other, the gasification chamber and the charcombustion chamber are fully divided from each other by the partitionwall above the interface of the fluidized bed, and the intensity of thefluidized state in the gasification chamber near the partition wall andthe intensity of the fluidized state in the char combustion chamber arekept in a predetermined relationship. Therefore, the fluidizing mediumis moved from the char combustion chamber through the opening providedin the partition wall near the furnace bottom into the gasificationchamber, and the fluidizing medium is moved from the gasificationchamber into the char combustion chamber.

In this embodiment, since the gasification chamber and the charcombustion chamber are fully divided from each other by the partitionwall above the interface of the fluidized bed, even when the gaspressures in these chambers are changed, gas seal between these chambersis kept, and the combustion gases and the generated gases are preventedfrom being mixed with each other. Therefore, no special control isrequired to achieve a gas seal between the gasification chamber and thechar combustion chamber. By keeping the predetermined intensity of thefluidized state in the gasification chamber near the partition wall andthe intensity of the fluidized state in the char combustion chamber, thefluidizing medium can stably be moved in a large amount from the charcombustion chamber through the opening provided in the partition wallnear the furnace bottom into the gasification chamber. Therefore, nomechanical means for handling high-temperature particles is required tomove the fluidizing medium from the char combustion chamber into thegasification chamber.

In the integrated gasification furnace, a weakly fluidized region in thechar combustion chamber which is in contact with the gasificationchamber may serve as the settling char combustion chamber, which may beseparated from the major part of the char combustion chamber by thepartition wall which extends from the furnace bottom to a position nearthe interface of the fluidized bed. A strongly fluidized region and aweakly fluidized region may be defined in each of the char combustionchamber, the settling char combustion chamber, and the gasificationchamber for producing internal revolving flows of the fluidizing mediumin each of the chambers.

In the above integrated gasification furnace, the heat recovery chambermay be disposed in contact with the strongly fluidized region in thechar combustion chamber, the heat recovery chamber and the charcombustion chamber may have openings near the furnace bottom, and may bedivided from each other by the partition wall whose upper end reaches aposition near the interface of the fluidized bed, and the fluidizedstate in the char combustion chamber near the partition wall may berelatively stronger than the fluidized state in the heat recoverychamber to produce forces to circulate the fluidizing medium.Alternatively, the heat recovery chamber may be disposed in contact withthe strongly fluidized region in the settling char combustion chamber,the heat recovery chamber and the settling char combustion chamber mayhave openings near the furnace bottom, and may be divided from eachother by the partition wall whose upper end reaches a position near theinterface of the fluidized bed, and the fluidized state in the settlingchar combustion chamber near the partition wall may be relativelystronger than the fluidized state in the heat recovery chamber toproduce forces to circulate the fluidizing medium.

The fluidizing gas in the gasification chamber comprises an oxygen-freegas. The oxygen-free gas may comprise a gas which does not containoxygen at all, e.g., water steam or the like.

The furnace bottom in each of the gasification chamber, the charcombustion chamber, and the heat recovery chamber may be slanted alongthe flow patterns of the fluidizing medium in the vicinity of thefurnace bottom. The temperature of the gasification chamber may beadjusted by controlling the fluidized state in the weakly fluidizedregion in the char combustion chamber which is in contact with thegasification chamber.

FIG. 4 shows an embodiment in which the present invention is applied toa cylindrical furnace having a vertical axis. A cylindrical integratedgasification furnace 10 houses a cylindrical partition wall 10 aconcentric with an outer wall thereof, the partition wall 10 a defininga char combustion chamber 2 therein. Settling char combustion chambers4, a gasification chamber 1, and a heat recovery chamber 3, each havinga sectorial shape (a shape bounded between two radius in an annular areadefined between two concentric circles), are disposed in an annular areaextending outside of the partition wall 10 a surrounding the charcombustion chamber 2. The gasification chamber 1 and the heat recoverychamber 3 are positioned opposite to each other with the settling charcombustion chambers 4 interposed therebetween. The gasification furnacehaving the above cylindrical shape can easily be housed in a pressurevessel as with an integrated gasification furnace shown in FIG. 11. Theintegrated gasification furnace 10 has a basic structure that is similarto the gasification furnace 101 shown in FIG. 1, except that it ispressurized and is arranged so that it can easily be housed in apressure vessel 50.

FIG. 5 is a horizontal cross-sectional view of a fluidized bed in theembodiment shown in FIG. 4. The char combustion chamber 2 is positionedat the center, the gasification chamber 1 at a peripheral area, and theheat recovery chamber 3 opposite to the gasification chamber 1, with thetwo sectorial settling char combustion chambers 4 being interposedbetween the gasification chamber 1 and the heat recovery chamber 3.There are a plurality of gas diffusers positioned at the furnace bottomof the sectorial gasification chamber 1, which has strongly fluidizedregions 1 b at its opposite ends for providing an increased spacevelocity and a weakly fluidized region 1 a at its center for providing areduced space velocity. The fluidizing medium in the gasificationfurnace forms internal revolving patterns which rise in the stronglyfluidized regions 1 b and settle in the weakly fluidized region 1 a. Therevolving flows diffuse a fuel F charged into the gasification furnace 1wholly in the gasification furnace 1, which is thus effectivelyutilized.

The fluidizing gas in the gasification furnace 1 comprises mainly agenerated gas in recycled use or a gas free of oxygen, such as watersteam or a combustion exhaust gas. When the temperature of thegasification chamber is excessively reduced, oxygen or an oxygencontaining gas, e.g., air, may be mixed with the fluidizing gas. Apartition wall 11 between the gasification chamber 1 and the charcombustion chamber 2 has an opening 21 provided therein near the furnacebottom, and fully divides the gasification chamber 1 and the charcombustion chamber 2 from each other up to the ceiling except for theopening 21. The fuel F which is pyrolyzed and gasified in thegasification chamber 1 flows through the opening 21 into the charcombustion chamber 2. The opening 21 may be provided fully across thegasification chamber 1, or may be provided only in the weakly fluidizedregion. In FIG. 5, black arrows indicate paths of movement of thefluidizing medium in settling flows through openings in the partitionwalls at the furnace bottom, and gray arrows indicate paths of movementof the fluidizing medium in rising flows over the upper ends of thepartition walls.

The operating temperature of the gasification furnace 1 can be adjustedto an optimum temperature with each fuel. If the fuel has a relativelylow gasification rate and produces a large amount of char, such as coal,then the gasification furnace 1 can obtain a high gasification rate bymaintaining a temperature ranging from 800 to 900° C. therein. If thefuel produces a small amount of char, such as municipal waste, then thegasification furnace 1 can obtain a stable operation while removingchlorine and controlling a volatile release rate, by maintaining a bedtemperature in the range from 350 to 450° C.

The gas diffusers at the furnace bottom of the char combustion chamber 2are divided into those at a central region and those at a peripheralregion, and diffuse the fluidizing gases such that the central regionforms a weakly fluidized region 2 a and the peripheral region forms astrongly fluidized region 2 b. The strongly fluidized region 2 b formstherein a rising fluidized bed in which the fluidizing medium ascendsand the weakly fluidized region 2 a forms therein a settling fluidizedbed in which the fluidizing medium descends.

The char combustion chamber 2 should be maintained at as high atemperature as possible, preferably at a bed temperature of around 900°C., for promoting char combustion and supplying sensible heat to thegasification chamber 1. In the case of fluidized bed combustionaccompanying an endothermic reaction therein, generally, the possibilityof agglomeration formation increases in the operation at a temperatureof around 900° C. In this embodiment, however, the revolving flows inthe char combustion chamber promote heat diffusion and char diffusion,making it possible to combust char stably without agglomerationformation. The agglomeration refers to a solidified lump originated inmelted ash of the fluidizing medium and the fuel.

The settling char combustion chambers 4 should preferably be kept whollyin a weakly fluidized state in order to form a settling fluidized layer.However, as shown in FIG. 4, each of the settling char combustionchambers 4 may have a weakly fluidized region 4 a and a stronglyfluidized region 4 b for promoting heat diffusion, and an internalrevolving flow may be produced to form a settling fluidized layer in aregion being in contact with the gasification furnace 1.

In this embodiment, as shown in FIG. 4, partitions 16 between thesettling char combustion chambers 4 and the heat recovery chamber 3 havetheir lower ends reach the furnace bottom and their upper ends locatedin a position much higher than the interface of the fluidized bed forpreventing the fluidizing medium from flowing between the settling charcombustion chambers 4 and the heat recovery chamber 3. This is becausefor a fuel containing high fixed carbon such as coal, the fluidizingmedium flowing from the settling char combustion chambers into thegasification chamber should preferably have a temperature which is ashigh as possible, and it is not preferable for the fluidizing mediumcooled in the heat recovery chamber 3 to be mixed with thehigh-temperature fluidizing medium that is to flow into the gasificationchamber 1, or for the high-temperature medium to flow into the heatrecovery chamber 3.

In the case that the integrated gasification furnace according to thisembodiment is used for gasification combustion of waste materials, thepartition walls 16 may have upper ends positioned near the interface ofthe fluidized bed, and openings provided therein near the furnace bottomfor causing the fluidizing medium to circulate between the settling charcombustion chambers 4 and the heat recovery chamber 3. This is becausefor a fuel which produces char at a low rate, such as wastes, thecombustion temperature in the char combustion chamber cannot bemaintained unless the temperature of the gasification chamber is loweredto reduce the gas production rate. In this case, as shown in FIG. 6, agas diffuser at the furnace bottom of the heat recovery chamber 3 isdivided, and the heat recovery chamber 3 is separated by partition walls16 a for using one part with the char combustion chamber and anotherpart as the settling char combustion chamber, so that the temperaturesof the char combustion chamber and the gasification chamber can becontrolled independently of each other. A gas diffuser at the furnacebottom of each of the settling char combustion chambers 4 may be dividedfor forming strongly fluidized regions 4 b in contact with the heatrecovery chamber 3.

Radial submerged heat transfer pipes 41 are disposed in the heatrecovery chamber 3. The fluidizing medium flowing from the charcombustion chamber 2 beyond the partition wall 12 is cooled by the heattransfer pipes 41, and then returns through the opening 22 in the lowerportion of the partition wall 12 back into the char combustion chamber2. Since the pitch or spacing of the submerged heat transfer pipesextends toward the peripheral region, the resistance charged to thefluidizing medium which flows across the submerged heat transfer pipesis smaller in the peripheral region. Therefore, the fluidizing mediumflowing into the char combustion chamber 2 is uniformly dispersed in theperipheral region, resulting in effective utilization of the entirevolume of the heat recovery chamber 3. Therefore, the integratedgasification furnace is of a compact structure as a whole.

FIG. 7 shows a rectangular furnace which embodies the integratedgasification furnace according to the present invention. When theintegrated gasification furnace is used under atmospheric pressure, theouter wall of the gasification furnace is not required to have awithstand-pressure structure. For this reason, the rectangular furnaceis preferable also from a viewpoint of manufacturing.

In the case that the fuel type is suitable for operating the integratedgasification furnace at a reduced temperature, as shown in FIG. 7, theheat recovery chamber 3 is divided into the char combustion chamber andthe settling char combustion chamber by partition walls 13, 16, so thatthe temperature of the fluidizing medium to be supplied to thegasification chamber 1 can be controlled independently from thetemperature in the char combustion chamber 2.

In the rectangular furnace shown in FIG. 7, both the fluidizing mediumin the weakly fluidized region in the char combustion chamber 2 and thefluidizing medium in the heat recovery chamber 3 which is in contactwith the weakly fluidized region in the char combustion chamber 2 are inthe weakly fluidized state. Therefore, the fluidizing medium does nothave a definite direction to move in, and may not effectively performits function as a heat medium. In such a case, as shown in FIG. 8, theregion of the heat recovery chamber 3 which is in contact with theweakly fluidized region in the char combustion chamber 2 may be openedoutwardly of the furnace, and the open region may be used effectively,e.g., by providing a supply port for recycled char.

FIG. 9 shows an embodiment in which the present invention is applied toan atmospheric-pressure-type fluidized-bed furnace.

In this embodiment, even if the fuel contains chlorine, the submergedheat transfer pipes 41 in the heat recovery chamber 3 and heat transferpipes 42 in the freeboard of the char combustion chamber are not almostexposed to the chlorine, so that the steam temperature can be increasedto 350° C. or higher, which is the maximum steam temperature in aconventional waste incinerator, or even to 500° C. or higher. In aregion where the combustion gases are blown from the char combustionchamber 2 into the gasification chamber 1, remaining oxygen in thecombustion gases reacts with combustible gases, resulting in a hightemperature. In this region, therefore, the combustion of the char andthe decarboxylation of limestone are promoted for enhancing combustionefficiency and desulfurization efficiency. A pressure loss caused whenthe combustion gases are blown from the char combustion chamber 2 intothe gasification chamber 1 ranges from about 200 to 400 mmAq. Since thehead of the fluidized bed from the lower end of the partition wall 15 tothe interface of the fluidized bed is normally in the range from 1500 to2000 mmAq, a pressure difference can automatically be maintained whenthe bed height in the gasification chamber is slightly lower than thebed height in the char combustion chamber, as shown in FIGS. 3A and 3B,and hence no special control is required.

FIG. 10 shows a process flow for melting ash by using a gas generated inthe integrated gasification furnace according to the present invention.In this embodiment, the furnace 10 at atmospheric pressure has thegasification chamber 1, the char combustion chamber 2, the heat recoverychamber 3, and the settling char combustion chamber 4 provided therein.When a large amount of fluidizing medium is circulated through thesechambers, the integrated gasification furnace operates stably in thesame manner as the above embodiments. In this embodiment, part of thepyrolysis gases from the gasification chamber 1 is introduced into aslagging combustion furnace 54 for melting the ash. A waste boilerremoves heat from the remaining pyrolysis gases together with the charcombustion gas, and the remaining pyrolysis gases are dedusted by adeduster 52, and then discharged outside.

FIG. 11 shows a combined cycle power generation system which employs theintegrated gasification furnace according to the present invention.

The integrated gasification furnace 10 is disposed in a pressure vessel50 and operated under pressurized condition. The integrated gasificationfurnace 10 may have an integral structure such that the outer wall ofthe integrated gasification furnace 10 works as the pressure vessel.Part of the combustible gases generated in the gasification furnace 1 issupplied to a slagging combustion furnace 54 under normal pressure, andused as the heat for melting ash. Remaining combustible gases, togetherwith the char combustion gases, are dedusted by a high-temperature dustcollector 51, and then led to a topping combustor 53 as a stabilizingcombustion chamber, which generates high-temperature exhaust gases to besupplied to a gas turbine 55 as an energy recovery device. The gasturbine 55 has a structure identical to a gas turbine of an ordinary gasturbine unit, and is called a power recovery turbine.

Heat transfer pipes 42 may be installed in an upper portion of the charcombustion chamber 2. Even if the fuel contains chlorine, since almostall of the chlorine is contained in gases generated in the gasificationfurnace 1, the char combustion gases contain almost no chlorine in thisembodiment. Therefore, the heat transfer pipes 42 may be used as a steamsuperheater to superheat steam at 500° C. or higher. Inasmuch assubmerged heat transfer pipes 41 installed in the heat recovery chamber3 are less exposed to a corrosive environment than the heat transferpipes 42, the submerged heat transfer pipes 41 may be used as a steamsuperheater to superheat steam at higher temperatures than the heattransfer pipes 42. If the concentration of chlorine, in the fuel isrelatively high, then since the concentration of chlorine in thecombustible gases is also high, the whole amount of combustible gases isled to the slagging combustion furnace 54 to prevent the toppingcombustor 53 and the gas turbine 55 from being corroded.

The power generation system which employs the pressurized fluidized-bedfurnace shown in FIG. 11 operates as follows. First of all, coal isgasified in the pressurized gasification furnace, and generated unburnedcarbon (so-called char) is combusted in the pressurized char combustionchamber 2. Combustion gases from the char combustion chamber 2 andgenerated gases from the gasification chamber 1 are respectively cleanedby the high-temperature dust collectors 51, 52, and then mixed andcombusted in the topping combustor 53, which produces high-temperaturegases to drive the gas turbine 55. Each of the high-temperature dustcollectors 51, 52 may comprise a ceramic filter, a metal filter ofheat-resisting alloy, a cyclone separator, or the like.

As for the power generation system which employs the pressurizedfluidized-bed furnace, it is important how the temperature of gasesflowing into the gas turbine 55 can be increased to an allowable maximumtemperature designed for each gas turbine. The greatest limitationimposed on increasing the temperature of gases flowing into the gasturbine 55 is cleaning of the generated gases. The cleaning of thegenerated gases is carried out by desulfurization, for example. Thedesulfurization is required to protect the blades of the gas turbine,for example.

For cleaning the generated gases, it is necessary to cool the generatedgases usually to about 450° C. in view of an optimum temperature for adesulfurizing reaction in a reducing atmosphere. On the other hand, thegas temperature at the inlet of the gas turbine should be as high aspossible because the efficiency of the gas turbine becomes higher as thegas temperature becomes higher. At present, it is ordinarily the case toincrease the gas temperature at the inlet of the gas turbine to 1200° C.or slightly lower due to limitations by heat resistance and corrosionresistance performances of the materials for the gas turbine. Therefore,the generated gases are required to have a calorific value high enoughto increase the gas temperature from 450° C. for the gas cleaning to1200° C. at the inlet of the gas turbine. Although not shown in FIG. 11,a generated gas cooler is provided in a gas line between thegasification chamber 1 and the high-temperature dust collector 52 forcooling the gases to 450° C., for example, and a desulfurizer is alsotypically provided in the gas line. However, a gas line from the charcombustion chamber does not need to have a gas cooler and a desulfurizerbecause limestone is charged into the furnace and circulated togetherwith the fluidizing medium and the char combustion chamber 2 is in anoxidizing atmosphere where oxygen is present, so that the sulfur contentis removed as CaSO₄.

Consequently, for the development of a power generation system using animproved pressurized fluidized-bed furnace, efforts should be made toobtain generated gases in as small an amount as possible and having ashigh a calorific value as possible. The reasons are as follows. If theamount of generated gases to be cleaned at 450° C. is reduced, the lossof sensible heat due to cooling is reduced, and a minimum requiredcalorific value of the generated gases may be lowered. In the case thatthe calorific value of the generated gases is higher than the calorificvalue needed to increase the gas temperature to the required gastemperature at the inlet of the gas turbine, the ratio of combustion aircan be increased to increase the amount of gases flowing into the gasturbine for a further increase in the efficiency of power generation.

In the system shown in FIG. 11, the combustion gases from the charcombustion chamber 2 are dedusted in the high-temperature dust collector51 which comprises a ceramic filter or the like, and then led to the gasturbine 55 for power recovery. While the combustion gases may bedirectly led to the gas turbine 55, the efficiency of power recovery maynot always be high because the temperature of the combustion gases isnot so high. Therefore, the combustion gases from the dust collector 51are led to the topping combustor 53. The generated gases (combustiblegases) from the gasification chamber 1 are dedusted in thehigh-temperature dust collector 52 which comprises a ceramic filter orthe like, and then led to the topping combustor 53 where they arecombusted. The combustion of the generated gases in the toppingcombustor 53 serves as stabilizing combustion for the combustion gasesfrom the char combustion chamber 2. Because of the combustion heatgenerated in the topping combustor 53, the combustion gases from thechar combustion chamber 2 (and the combustion gases used for stabilizingcombustion) become high-temperature gases at about 1200° C. (possibly1300° C., but depending on the heat-resistance of the gas turbine). Thehigh-temperature gases are supplied to the gas turbine (power recoverydevice) 55. The combination of the char combustion chamber 2 and thetopping combustor 53 corresponds to a combustor of an ordinary gasturbine unit.

The generator 57 connected to the rotating shaft of the gas turbinedirectly or through a speed reducer is driven to generate electricpower. In the embodiment shown in FIG. 11, a compressor (typically anaxial-flow air compressor) 56 is directly connected to the rotatingshaft of the gas turbine 55 for producing compressed air. The compressedair from the compressor 56 is supplied to the char combustion chamber 2as combustion air for the char combustion chamber 2. Part of thecompressed air is supplied to the topping combustor 53. However, thetopping combustor 53 can combust the generated gases with oxygen thatremains in the exhaust gases from the char combustion chamber 2. In thisembodiment, the interior of the pressure vessel 50 is pressurized to apressure ranging from 5 to 10 kg/cm² (0.5 to 1.0 MPa). However, theinterior of the pressure vessel 50 may be pressurized to about 30 kg/cm²(3.0 MPa) according to the specifications of the gas turbine 55.

In the embodiment shown in FIG. 11, since the combustion gases from thechar combustion chamber 2 and the generated gases from the gasificationchamber 1 are supplied to the gas turbine 55, the topping combustor 53is needed as a pre-mixing chamber for mixing these gases. In the casethat only the generated gases from the gasification chamber 1 are led tothe gas turbine 55, the generated gases may be introduced directly to acombustor 105 combined with a gas turbine unit 109 shown in FIG. 14which will be described later. In the case that only the generated gasesfrom the gasification chamber 1 are led to the gas turbine 55, the gasturbine 55 may be operated using highly calorific gases as a fuel.

The exhaust gases discharged from the gas turbine 55 are led via a line125 to a waste-heat boiler 58, from which the exhaust gases flow througha line 128, a desulfurizer, and a denitrater (not shown), and thenemitted from a stack (not shown).

The waste-heat boiler 58 recovers the heat of the exhaust gases andgenerates water steam. The generated water steam flows through a watersteam pipe 127 to a steam turbine 112. A generator 113 connected to therotating shaft of the steam turbine 112 directly or through a speedreducer is actuated to generate electric power. The water steam suppliedto the steam turbine 112 may include water steam from the heat transferpipes 41, 42.

FIG. 12 shows another embodiment in which the integrated gasificationfurnace according to the present invention is employed in a combinedcycle power generation system.

In the case that the fuel has a relatively high calorific value such ascoal, it is possible to raise the temperature to a temperaturesufficiently high to melt the ash without achieving complete combustionin the slagging combustion furnace. In this case, therefore, it iseffective to replace the slagging combustion furnace 54 with a slagginggasification furnace 60 for producing gases. The slagging gasificationfurnace should preferably be a gasification furnace of the type whichallows gases and slag to flow downwardly, heats the slag with the heatof the gases, and leads the gases into water to quench the gases whilepreventing the slag from failing flowability due to cooling. Theproduced gases thus obtained contain almost no chlorine, and can be usedas a raw material for chemicals and also as a gas turbine fuel. In theembodiment shown in FIG. 12, as with the embodiment shown in FIG. 11,the gas turbine 55 is connected to the topping combustor 53, and the aircompressor 56 and the waste-heat boiler 58 are provided. As with theembodiment shown in FIG. 11, furthermore, the steam turbine 1 12 and thegenerator 113 are used for power recovery.

An embodiment in which the normal-pressure-type integrated gasificationfurnace (normal-pressure ICFG) according to the present invention iscombined with a power recovery device will be described below withreference to FIG. 13. The system according to this embodiment is aso-called ICFG combined cycle power generation system. The gasificationchamber 1 of the integrated gasification chamber 101 described withreference to FIG. 1, for example, is connected with a generated gas line121 for delivering generated gases, a generated gas cooler 102 providedwithin the generated gas line 121, and a char collector 103, which arearranged in order. A conduit 122 is connected to a lower portion of thechar collector 103 for returning collected char to the char combustionchamber 2. The char collector 103 is connected with a conduit 123 forleading generated gases which have been cleaned by separating chartherefrom, to a combustion chamber 105 of a gas turbine unit. Agenerated gas compressor 104 is connected to the conduit 123 forincreasing the pressure of gases generated in the gasification furnaceat a normal pressure which is almost equal to an atmospheric pressure,to a pressure required for the gas turbine 106. The compressor 104 maybe a reciprocating compressor or a centrifugal compressor depending onthe flow rate and discharge pressure of the gases. Since the gases to becompressed are gases generated in the gasification furnace (i.e., a fuelwhich is in a relatively small quantity with a high calorific value) thepower of the compressor 104 is not so increased.

In this embodiment, the gas turbine unit 109 which serves as a firstenergy recovery device uses only generated gases with a high calorificvalue from the gasification chamber 1, independently of the combustiongases from the char combustion chamber 2. That is, the generated gasesare not mixed with the combustion gases from the char combustion chamber2 and are not used to heat the combustion gases, but are led as a fuelto the first energy recovery device independently of the combustiongases.

An air compressor 107 is directly coupled to the rotating shaft of thegas turbine 106. Air supplied by the air compressor 107 and thegenerated gases compressed by the compressor 104 are combusted in thecombustor 105, which produces combustion gases at a high temperature ofabout 1200° C. that are supplied to the gas turbine 106 to generatepower. A rotating shaft of a generator 108 is connected to the rotatingshaft of the gas turbine 106 directly or through a speed reducer forrecovering the power as electric power. The combustion gases (exhaustgases) from the gas turbine 106 are discharged via a line 125.

On the other hand, The combustion gases (exhaust gases) from the charcombustion chamber 2 and the heat recovery chamber 3 have sensible heatto be recovered, but do not have a calorific value as a fuel and apressure to be recovered as power. The combustion gases are dischargedvia a line 124. The line 124, 125 is joined into a line 126 connected toa waste-heat boiler 111. The waste-heat boiler 111 generates water steamwith the heat of the waste gases, and the generated water steam is ledvia a water steam pipe 127 to a steam turbine 112. The rotating shaft ofa generator 113 is connected to the rotating shaft of the steam turbine112 directly or through a speed reducer for recovering the power aselectric power.

The combustion gases (exhaust gases) at a lowered temperature, fromwhich the heat is recovered by the waste-heat boiler 111, flow through aline 128 and are cleaned by at least one of a desulfurizer, adenitrater, and a deduster, and are then emitted from a stack 115.

As shown in FIG. 15, the integrated gasification furnace 10 or 101 maybe connected to an existing boiler 131, rather than the new waste-gas(waste-heat) boiler 111. The difference between the amount of a fuelrequired by the existing boiler and the amount of generated gases andcombustion gases supplied by the integrated gasification furnace 101 maybe compensated for by supplying another fuel such as pulverized coal orthe like via a fuel supply line 132. In this manner, it is possible toprovide an apparatus for recovering power from generated gases andrecovering remaining energy from exhaust gases inexpensively. With thisarrangement, an existing boiler which discharges a CO₂ gas in arelatively large amount with respect to an energy such as generatedelectric power, can be converted into a highly efficient system. This isthe repowering of the existing boiler.

In the above embodiment, the gas turbine 106 of the gas turbine unit isemployed as a power recovery device which is an energy recovery device.However, a diesel engine which uses a gas fuel may be employed dependingon the amount of generated gases as a fuel.

An embodiment in which the pressurized-type integrated gasificationfurnace according to the present invention is combined with a powerrecovery device will be described below with reference to FIG. 14.According to this embodiment, whereas the normal-pressure-typeintegrated gasification furnace shown in FIG. 13 operates substantiallyunder the atmospheric pressure, the integrated gasification furnace 10is disposed in the pressure vessel 50 and operates under a pressurehigher than the atmospheric pressure. This is a feature that isidentical to that of the integrated gasification furnace shown in FIG.11. Since the gasification furnace 1 is under pressure, the gascompressor 104 is not required to supply the generated gases to the gasturbine unit 109, unlike the embodiment shown in FIG. 13. Therefore, thegas compressor 104 is not provided in the line 123. However, if the gasturbine comprises a standard-type gas turbine and its operating pressureis higher than the pressure of the pressurized-type integratedgasification furnace, then a gas compressor is employed to raise apressure for making up for the pressure difference. The compressionratio of such a gas compressor may be lower than that in the case ofFIG. 13.

Since the combustion gases from the char combustion chamber 2 have apressure higher than the atmospheric pressure, the combustion gases areled via a line 124 to a dust collector 110 such as a ceramic filter orthe like. After the combustion gases are cleaned by the dust collector110, the compression gases are supplied to a power recovery turbine 141as a second energy recovery device. The power recovery turbine 141 has astructure which is identical to that of the gas turbine of an ordinarygas turbine unit. An air compressor (typically an axial-flow aircompressor) 142 is directly connected to the rotating shaft of the powerrecovery turbine 141. The compressed air from the compressor 142 is usedas a fluidizing air in the char combustion chamber 2 and the heatrecovery chamber 3. A generator 143 is connected to the rotating shaftof the power recovery turbine 141 directly or through a speed reducerfor generating electric energy.

The exhaust gases, from which the pressure energy has been recovered bythe power recovery turbine 141, are discharged via a line 131, combinedwith exhaust gases from the gas turbine 106 via the line 125, and areled to the waste-heat boiler 111. Other details of the embodiment shownin FIG. 14 are identical to the embodiment shown in FIG. 13, and willnot be described below.

As shown in FIG. 16, the waste-heat boiler 111 shown in FIG. 14 maycomprise an existing boiler which uses pulverized coal as a fuel. Therelationship between the embodiment shown in FIG. 16 and the embodimentshown in FIG. 14 is the same as the relationship between the embodimentshown in FIG. 15 and the embodiment shown in FIG. 13.

According to the present invention, as described above, since the fuelin the gasification chamber is gasified in the fluidized bed which ismade of the high-temperature fluidizing medium that flows from the charcombustion chamber, the gases discharged from the gasification chamberare mostly either gases only generated from the fuel or a mixture ofgases generated from the fuel and fluidizing gases for the gasificationchamber, and hence have a high calorific value. Since the charcombustion gases and the generated gases are not mixed with each other,gases having a high calorific value can be obtained, and an energy suchas power can be recovered from the generated gases by the energyrecovery device.

It is possible to easily obtain high-temperature gases which are mixedwith the char combustion gases and lead to the energy recovery device,typically the power recovery device such as a gas turbine, forincreasing the energy recovery efficiency of power generation or thelike. Even if the fuel is any of various fuels containing volatilecomponents at largely different ratios, since the temperature of thechar combustion chamber and the gasification chamber can easily becontrolled, the fuel can be used without any equipment modification.

Even if a fuel such as municipal waste containing chlorine is used, mostof the chlorine in the fuel is discharged into gases in the gasificationchamber and does not remain in the char that flows into the charcombustion chamber. Therefore, the chlorine concentration in the gasesin the char combustion chamber and the heat recovery chamber is kept atan extremely low level. Even when the submerged pipes in the heatrecovery chamber are used as superheater pipes to recoverhigh-temperature steam, there is no risk of heat corrosion. Thus, thehigh-temperature steam recovery, together with the energy recovery withthe power recovery device, makes it possible to recover energy with highefficiency.

Industrial Applicability

The present invention is profitable for a system which gasifies andcombusts fuels including coal, municipal waste, etc., and recoversenergy therefrom.

1. A gasification furnace comprising: a gasification chamber forpyrolyzing and gasifying a fuel to produce combustible gas and char; achar combustion chamber for combusting the char supplied from saidgasification chamber; a partition wall for dividing said gasificationchamber and said char combustion chamber, said partition wall having asupply opening located below an interface of a fluidized bed of saidgasification furnace for allowing a fluidizing medium and the char to besupplied directly from said gasification chamber to said char combustionchamber; a furnace bottom slanted downward toward said supply opening;and a settling char combustion chamber provided in said char combustionchamber for allowing the fluidizing medium to descend to a returnopening located below the interface of the fluidized bed of saidgasification furnace, the fluidizing medium being returned from saidchar combustion chamber to said gasification chamber through said returnopening after the fluidizing medium descends in said settling charcombustion chamber.
 2. A gasification furnace according to claim 1,wherein said return opening and said supply opening are located below anupper surface of a dense bed of said gasification furnace.
 3. Agasification furnace according to claim 1, wherein said return openingand said supply opening are located near said furnace bottom of saidgasification furnace
 4. A gasification furnace according to claim 1,further comprising an incombustible material discharging port fordischarging incombustible material from said gasification furnace.
 5. Agasification furnace according to claim 1, wherein said partition wallcomprises a first partition wall and a second partition wall having alower end in contact with said furnace bottom of said gasificationfurnace and an upper end located at the interface of the fluidized bed.6. A gasification furnace according to claim 1, wherein an internallyrevolving flow of the fluidized medium is formed in said gasificationchamber.
 7. A gasification furnace comprising: a gasification chamberfor pyrolyzing and gasifying a fuel to produce combustible gas and char;a char combustion chamber for combusting the char supplied from saidgasification chamber; a settling gasification chamber provided in saidgasification chamber for allowing a fluidizing medium and the char todescend to a supply opening located below an interface of a fluidizedbed of said gasification furnace, the fluidizing medium and the charbeing supplied from said gasification chamber to said char combustionchamber through said supply opening after the fluidizing medium and thechar descend in said settling gasification chamber, a furnace bottomslanted downward toward said supply opening; and a partition wall fordividing said char combustion chamber and said gasification chamber,said partition wall having a return opening located below the interfaceof the fluidized bed of said gasification furnace for allowing thefluidizing medium to be returned directly from said char combustionchamber to said gasification chamber.
 8. A gasification furnaceaccording to claim 7, wherein said return opening and said supplyopening are located below an upper surface of a dense bed of saidgasification furnace.
 9. A gasification furnace according to claim 7,wherein said return opening and said supply opening are located nearsaid furnace bottom of said gasification furnace.
 10. A gasificationfurnace according to claim 7, further comprising an incombustiblematerial discharging port for discharging incombustible material fromsaid gasification furnace.
 11. A gasification furnace according to claim7, wherein an internally revolving flow of the fluidized medium isformed in said gasification chamber.